Temperature mapping of storage areas Technical supplement to who technical Report Series, No. 961, 2011

WHO Expert Committee on Specifications for Pharmaceutical Preparations
2.4.3 
Mean temperatures 
Arithmetic mean temperatures can be applied to each of the separate areas being 
monitored over the study period. These mean temperature measurements can be 
useful in storage areas where the temperature fluctuates with time in a repetitive 
pattern (e.g. sinusoidal fluctuation or periodic peak occurrence) and where the 
temperature also varies depending upon the location of the data logger.
The use of mean temperatures enables the analyst to determine a mean 
temperature for a given EDLM location over the study period. These figures can 
then be compared between all the EDLM locations within the space. This enables 
the analyst to identify the locations where the mean temperatures are consistently 
lower or higher, an outcome that cannot be achieved simply by comparing 
individual data points.
In Figure 3, the minimum and maximum temperatures have been 
calculated from the data points for two locations (EDLM-1 and EDLM-2). The 
plot shows that the EDLM-2 location is clearly cooler on average, although 
there are also times when the two locations experience similar low and 
high temperatures.
Despite the usefulness of mean figures, it is essential not to disregard 
the actual temperature data because these figures reveal the occurrence of 
temperatures that are outside the specified storage temperature range.
2.4.4 
Interpreting the results and making recommendations
This section outlines how to interpret the results, and how to use these results to 
support the report’s recommendations:
■
Document the internal temperature variations observed within 
the space, taking account of the EDLM reading errors specified by 
the device manufacturer.
■
Use the data analysis to assess the overall temperature stability 
of the mapped space in relation to the stated acceptance criteria 
(if any).
■
Assess the overall thermal stability of the space during the study 
period with specific reference to the high and low temperatures 
experienced.
■
List the factors that explain the observed temperature variations. 
For example, the location of the heating and cooling components 
and doors.
12
12
Thermal stability will be affected by three main factors: the external ambient temperature; the type of 
building construction and the performance of the heating or cooling system. The first two factors are less 
significant for freezer rooms and cold rooms built inside an existing structure.

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WHO Technical Report Series, No. 992, Annex 5 
Supplement 8
■
Assess consistent and inconsistent temperature variations and 
fluctuations within the space in terms of their potential impact on 
product storage.
■
Based on the observed temperature fluctuations at the mapped 
locations within the space, make recommendations about the 
optimum storage locations for highly sensitive products, and those 
that are less sensitive. 
■
Based on the observed temperature fluctuations at the mapped 
locations within the space, make recommendations on the optimum 
location of the temperature sensor(s) used for routine temperature 
monitoring and the control sensors used to activate the heating and 
cooling systems.
Figure 3